Similar to positive pressure, a negative pressure or vacuum may be used to assist in the performance of a variety of functions. To generate a vacuum, a device is typically employed to remove at least some portion of a gas present in a sealed volume.
In motor vehicles, vacuum is often used to generate a load assist for actuation of various on-board systems, such as vehicle brakes. When employed to assist in the actuation of motor vehicle brakes, a booster device or a vacuum servo is used to accumulate and store the vacuum. The stored vacuum is subsequently used to multiply the braking force applied by an operator at the brake pedal, thereby decreasing the effort the operator is required to exert during braking of the vehicle.
Depending on the type of engine or other powerplant employed by a particular motor vehicle, either the engine's manifold vacuum or a separate vacuum pump may be used to provide a vacuum for accumulation by the booster device. If a vacuum pump is used in the motor vehicle, it is typically driven directly by the engine.